* Astronomy

Members Login

Post Info

TOPIC: Thera

Blobrana

L

Posts: 131433

Date: Aug 28 21:04 2006

RE: Thera	Permalink

The late Greek archaeologist Spyridon Marinatos in 1939 proposed that the eruption, a scant 70 miles away from Crete, caused the end of the Minoan civilization. The total volume of material belched from the eruption was a mile-square pile of dirt stacked nine miles high, making the blast about 120 times more powerful than the 1980 eruption of Mount St. Helens. The survey shows the Santorini Islands are surrounded by 530 square miles of volcanic rock on the ocean floor, in places close to the coast up to 260 feet thick. The rock likely rode across the ocean waves at the time of the eruption, a superheated "pyroclastic" wave of light ash and pumice. In its extent, it exceeded the 1815 Tambora eruption that killed 36,000 in Indonesia, the study concludes, the previous record holder. Ash, pyroclastic flow and tsunami likely combined to similar, deadly effect in the Mediterranean. The undersea survey also shows the nearby undersea volcano, Kolumbo, the largest of 20 volcanic cones around the islands, is still very much alive. An unexpected "widespread hydrothermal vent field was discovered on the floor of the Kolumbo submarine crater," the study says. Using robotic submersibles run by noted Titanic explorer, Robert Ballard, the team peeked 1,500 feet down into Kolumbo. The floor of the crater is covered with bacterial mats, scattered among the vents, some of them belching 428-degree Fahrenheit steam. Sulphur-rich deposits of lead, iron and precious metals cover the vents. The key issue for scholars in evaluating the volcano's effect is in resolving a dispute over the exact time of the eruption, Cline says. Some archaeologists, based on pottery and ancient Egyptian inscriptions, put the date at 1500 B.C. Experts in radiocarbon dating put it further back, to at least 1600 B.C. In April, a pair of new radiocarbon reports in Science magazine, one based on leaves and twigs buried in the eruption, overlapped to pin the date to between 1613 to 1627 B.C. Egyptologists such as Manfred Bietak of Austria's University of Vienna told Science they were unimpressed with the new dates however, so the debate continues. Source __________________

Blobrana

L

Posts: 131433

Date: Aug 24 23:39 2006

Santorini	Permalink

An international team of scientists has found that the second largest volcanic eruption in human history, the massive Bronze Age eruption of Thera in Greece, was much larger and more widespread than previously believed. During research expeditions in April and June, the scientists from the University of Rhode Island and the Hellenic Centre for Marine Research found deposits of volcanic pumice and ash 10 to 80 meters thick extending out 20 to 30 kilometres in all directions from the Greek island of Santorini. "These deposits have changed our thinking about the total volume of erupted material from the Minoan eruption" - Haraldur Sigurdsson, URI volcanologist. In 1991 Sigurdsson and his URI colleague Steven Carey had estimated that 39 cubic kilometres of magma and rock had erupted from the volcano around 1600 B.C., based on fallout they observed on land. The new evidence of the marine deposits resulted in an upward adjustment in their estimate to about 60 cubic kilometres. (The eruption of Mount Tambora in Indonesia in 1815 is the largest known volcanic eruption, with approximately 100 cubic kilometres of material ejected.) An eruption of this size likely had far-reaching impacts on the environment and civilizations in the region. The much-smaller Krakatau eruption of 1883 in Indonesia created a 100-foot-high tsunami that killed 36,000 people, as well as pyroclastic flows that travelled 40 kilometres across the surface of the seas killing 1,000 people on nearby islands. The Thera eruption would likely have generated an even larger tsunami and pyroclastic flows that travelled much farther over the surface of the sea. "Given what we know about Krakatau, the effects of the Thera eruption would have been quite dramatic. The area affected would have been very widespread, with much greater impacts on the people living there than we had considered before" - Steven Carey, a co-leader of this year's expeditions. Thera has erupted numerous times over the last 400,000 years, four of which were of such magnitude that the island collapsed and craters were formed. Some scientists believe the massive eruption 3,600 years ago was responsible for the disappearance of the Minoan culture on nearby Crete. Others link the eruption to the disappearance of the legendary island of Atlantis. While investigating the seafloor around Santorini, the scientists explored the submarine crater of the Kolumbo volcano, just 5 kilometres from Thera and part of the same volcanic complex, and discovered an extensive field of previously unknown hydrothermal vents. Using remotely operated vehicles from the Institute for Exploration, the scientists recorded gases and fluids flowing from the vents at temperatures as high as 220 degrees Centigrade. "Most of the known vents around the world have been found on the mid-ocean ridges in very deep water and in areas where there are geologic plate separations. The Kolumbo and Santorini volcanoes are in shallow water at plate convergences, the only place besides Japan where high-temperature vents have been found in these conditions" - Haraldur Sigurdsson "The high temperature of the vents tells us that the volcano is alive and healthy and there is magma near the surface" - Steven Carey. The scientists said that, in addition to fluids and gases, the vents are emitting large quantities of metals, including silver, which precipitate out to form chimneys on the crater floor up to 10 feet tall and 2 to 4 feet wide. The floor of the crater is covered in a layer of red and orange mats of bacteria 2 to 3 inches thick that live on the nutrients in the vent fluids. Bacteria also cover the vent chimneys, and 4- to 5-inch long, hair-like bacterial filaments extend from the chimneys making them "look like hairy beasts, like woolly mammoths," according to Sigurdsson. The expedition was part of a longer research cruise led by National Geographic Explorer-in-Residence Robert Ballard, a URI oceanography professor and president of the Institute for Exploration, which included a search for Bronze Age shipwrecks in the Black Sea and a survey of the seafloor in the Sea of Crete. The research expeditions were funded in large part by the National Science Foundation, with additional support from the NOAA Office of Ocean Exploration, the Rhode Island Endeavor Program, the Institute for Exploration, and the National Geographic Society. The April expedition was conducted aboard the Greek research vessel Aegaeo, while the June cruise was aboard the URI vessel Endeavor. Live video of the June expedition was broadcast over the internet 24 hours a day by Immersion Presents, which also broadcast four, 30-minute live programs each day to museums, school districts, science centres and Boys and Girls Clubs featuring Sigurdsson, Carey and Ballard. Read more __________________

Blobrana

L

Posts: 131433

Date: Apr 29 11:09 2006

Thera	Permalink

A single olive branch may have solved one of ancient history's most enduring mysteries - when and why did the great Minoan civilisation of the Mediterranean come to a sudden end? The olive branch was buried alive during a cataclysmic volcanic eruption on the Aegean island of Thera - now known as Santorini - and scientists believe they can date the precise moment of the tree's death. Knowing when the Thera disaster occurred is important because the volcanic eruption was so immense that it almost certainly caused the collapse of the Minoan civilisation which was centred on the nearby island of Crete. Longitude:, 25°23'50.03"E Latitude:, 36°24'10.35"N Volcanologists estimate that the Thera explosion generated violent tsunamis that thrashed Crete's ports, threw thousands of tons of ash, pumice and other debris into the atmosphere and created a "nuclear winter" that led to successive crop failures in the region. Scientists have detected ash from the explosion as far away as Greenland in the West, the Black Sea in the east and Egypt in the south. They have also discovered signs of frost damage caused by the volcano on preserved plant material excavated as far apart as Ireland and California. Walter Friedrich of the University of Aarhus in Denmark and his colleagues have analysed the olive branch's growth rings and combined the findings with radio-carbon dating to show that the tree must have died between 1627BC and 1600BC. "It is important to have a very precise date for the explosion because this eruption is a global time marker. If we can date it precisely we have an important tool to correlate the times of different cultures" - Dr Walter Friedrich . Tom Pfeiffer, a graduate student of Dr Friedrich, discovered the olive branch buried inside a rock face formed from volcanic debris. The researchers are convinced that the tree was still alive when it was smothered. The scientists found a sequence of 72 growth rings, including the final year's growth ring, inside the branch. They dated each growth ring with radio-carbon dating and worked out the year of the tree's death, to an accuracy of 13 years each way. The study, published in the journal Science, suggests that Thera blew apart about a century or so prior to the conventional date when the Minoan civilisation was thought to have gone into demise based on evidence from pottery and other archaeological objects. The scientists suggest that it is highly unlikely that the Minoans were able to survive the environmental impact of such an immense volcanic eruption, which meant their civilisation ended between 100 and 150 years earlier than previously thought. This would mean that the Minoan civilisation was not contemporary with the New Kingdom of ancient Egypt - which began in the 16th Century BC - as many archaeologists believed. If the Minoan civilisation ended a century or so earlier than the New Kingdom, it means they lived at the time of the Hykos kings of ancient Egypt, whose ancestors came from the Levant, an area of the Middle East that was not thought to have had direct ties with the Minoans. A separate study also published in Science by Professor Sturt Manning of Cornell University in New York shows that radiocarbon dating of 127 objects recovered from the Theran town of Akrotiri - which was completely buried by the eruption - support the revised timescale of the volcanic explosion. Professor Colin Renfrew, the distinguished Cambridge archaeologist, said that the studies appear to provide convincing evidence to finally put a firm date on the Thera eruption. However, not all archaeologists are convinced that the eruption on Thera led to the immediate and sudden end of the Minoan culture. Source __________________

«First < 1 2 3 | Page of 3 sorted by

Volcano Island Crete

Create your own FREE Forum
Report Abuse